by Stephen Vermette
Department of Geography & Planning, SUNY Buffalo State
After a light morning snowfall covered the ground, my wife noticed an interesting pattern in our front yard. The trees appeared to cast white shadows!
This is just one kind of phenomenon I call snow shadows. There are many different types of these winter oddities, and some stretch into another season.
Linear snow shadows
The linear snow shadows that my wife spotted were caused by ground temperature. At the time of the photo above, the rising sun was shining from the upper right corner of the image (southeast). The areas in between the tree trunks were exposed to sunlight, which quickly raised the surface temperature, melting the veneer of snow on the forest floor. However, the tree trunks blocked the sunlight, keeping the ground behind them slightly colder, which allowed the snow to linger just long enough to give us this fleeting snapshot of linear snow shadows.
The case of reversing snow shadows
The outer snowless ring in the cold-to-warm-day photo above was puzzling. What would cause the snow to melt and form that snowless ring?
Upon inspection, I noted that the ring was made up of bare soil, whereas the snow inside the ring (nearest the tree trunk) was resting on a layer of mulch. At the time of the photo, the air temperature was above freezing (the day transitioning from cold to warm). Apparently, the bare soil warmed up quickly and melted the snow, but the mulch and the grass kept the ground cold a little longer, and retained the snow – giving us a snowless shadow between the mulch and grass. The pattern has everything to do with the different insulating qualities of mulch (nearest the tree) and bare ground (the outer ring).
An opposite pattern appeared a few days later, which you can see in the photo below. In the second case, the transition was from a warm to cold day – the mulch retained heat collected through the day, but the bare ground cooled quickly. Apparently the light snow that fell later in the day accumulated only on the cooler bare soil (minus a couple of foot prints).
Snow melt shadows
Appearing after a winter warm period, and especially in spring, the snowpack appears to recede from tree trunks, leaving what I‘ve termed a “snow melt shadow.”
In this case, a light-colored surface (such as snow) reflects the sun’s energy away, while a dark surface (such as a tree trunk) tends to absorb the sun’s energy. The result is that the tree trunk warms up, and the heat radiated from the trunk melts the nearby snow. Similar shadows may be found around boulders protruding from the snowpack.
I wasn’t the first to record these snow melt shadows. Charles E. Burchfield (1893-1967), a nationally recognized watercolorist from Western New York, shows typical snow melt shadows in “Dawn of Spring, ca. 1960s,” which you can see below, as well as in another watercolor called “Late Winter Dawn (1956-1965).”
The titles of the watercolors indicate that Burchfield noticed that the weather pattern was associated with the end of winter. With the strengthening of the spring sun, snow melt shadows are a sign of the approach of warmer seasonal weather.
Learn more about Charles E. Burchfield and his watercolors at the website of the Burchfield Penney Art Center.
Vestigial snow ring
We recognize the forsythia bush as an early spring bloomer. However, in the photo below, the forsythia isn’t covered in blooms. Blooms appear only on the bottom branches, forming a ring of blooms.
This ring of blossoms indicates the height of an early spring snowpack. At some point during budding, extremely cold temperatures killed off the buds that were exposed to the air, but the snowpack insulated the buried lower buds from a killing freeze. We may refer to this ring of blooms as a vestigial snow ring, the shadow of a past snowfall!
This is the way a meteorologist sees nature.
I’m interested in learning more about your winter observations. Please leave a comment below.
You can share photos of your observations on the Your Photos page of Buffalo-NiagaraGardening.com. Email your photo as an attachment to Connie@Buffalo-NiagaraGardening.com. Please include information for a caption, including your name, town and what we should notice about the photo.
Very nice article. Very informative.
Thank you. I always wondered why some years only the lower branches of my forsythia would bloom. I usually cut some branches to force inside and in the years where there is only bottom flowering, the forcing doesn’t work. Now I know why.
Very cool article. I have noticed all of the “snow shadows” but never knew the “why”. I will feel very smart explaining them to my grandchildren. Thanks!